/Engine/Source/Runtime/Engine/Classes/Engine/GameViewportClient.h
Check an axis movement received by the viewport. If the viewport client uses the movement, it should return true to consume it.
virtual bool InputAxis ( [FViewport](API\Runtime\Engine\FViewport) * Viewport, int32 ControllerId, [FKey](API\Runtime\InputCore\FKey) Key, float Delta, float DeltaTime, int32 NumSamples, bool bGamepad )